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Climate Change Trends in Bangladesh

Saleh A. Wasimi
CQ University, Rockhampton, Queensland 4702, Australia

Abstract/ Executive Summary:

A summary of climate change trends in some hydrologic aspects that have manifested so far in Bangladesh is presented and compared with the forecasts, especially as reported in the Fourth Assessment Report of IPCC (2007). Changes in distribution pattern of temperature are analysed with quantile regression. Precipitation in Bangladesh is abundant compared to many other parts of the world, but it is the temporal distribution of rainfall that can have more significant impact if changes do occur. Changes in temporal distribution can be captured through PCI (Ceballos-Barbancho et al, 2008). There are certain aspects of climate change attributable to global warming which is occurring outside the territorial boundaries of Bangladesh but will affect the nation nevertheless. One such aspect is the decline of accumulated snow in the Himalayas, which is a major source of freshwater in Bangladesh. Another aspect is sea-level rise. Sea level will continue to rise in this century and beyond even with emission control and mitigation measures. Bangladesh being a deltaic region is very vulnerable to sea-level rise.

Keywords: Climate change, IPCC projections, Statistical analysis, Water resources

Location: All over Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Weather/Climate

Objectives:

The study was carried out to observe the climate change trends in Bangladesh

Methodology:

To analyse trends in atmospheric temperature in Bangladesh, the country has been divided into four hydrological regions which are: northwest, southwest, northeast and southeast – these are the traditional hydrologic units. In the northwest region temperature data of Rangpur, Dinajpur, Bogra, Rajshahi and Pabna have been analysed. This region is now showing a slight rising trend in average temperature of 0.01⁰C per year. The rise appears fairly uniform because the slope calculated for the period 1950-80 is similar to the slope for the period 1981-2008. In the southwest region temperature data of Barisal, Faridpur, Jessore, Khulna and Satkhira were analysed. Over the long period of record there were no significant trends with any station. However, after 1980 a flat gradient in minimum temperature and a rising trend in maximum temperatures can be observed – the gradient increases as we move from inland towards the coast and from east to west. Satkhira had the highest gradient of 0.02⁰C/year and Faridpur and Jessore had the lowest gradient being less than 0.01⁰C/year. Barisal data is suspect because there is discontinuity and sudden jumps in the data, which puts in doubt if there is a gradient as we move along the coast from east to west. In the northeast region, temperature data of Dhaka, Mymensingh, Sylhet, Srimangal, Brahmanbaria, and Comilla were analysed. Dhaka shows a flat gradient in annual mean temperature during the period 1950-80 and then a rising gradient of 0.05⁰C/year. Mymensingh shows a flat trend during the period 1950-80 similar to Dhaka and then a rising trend of 0.02⁰C/year. Dhaka is a much bigger metropolitan area with much higher growth rate compared to Mymensingh. Sylhet showed a falling trend during the period 1950-1980 of -0.01⁰C/year and a rising trend of 0.03⁰C/year after 1980. Observation in Brahmanbaria and Comilla shows a flat gradient during the period 1950-1980 and sufficient records after that period are not available to make any inferences about the trend. In the southeast region data of Maijdi Court, Chittagong, Rangamati and Cox’s Bazar were analysed. Except Rangamati all the stations are in the coastal area. All three coastal stations showed similar falling trend during 1950-80 period of -0.02⁰C/year and then a rising trend of 0.06⁰C/year. Rangamati showed a rising trend during 1950-65 and then a falling trend of -0.04⁰C/year which continued beyond 1980. In general, it appears that all along the coast the temperature is rising faster than inland over the years after 1980. If we look at a very long record of data that is available for Calcutta, we can see a rising trend of 2⁰C per century until 1950, a fall of 0.5⁰C from 1950 to 1980 and then a rise of 0.04⁰C/ year. It should be noted that Bangladesh faces the opposing effects of global warming and global dimming quite noticeably – the mostly alluvial terrain puts in lot of dust in the atmosphere which contributes significantly to dimming.

To determine trends in distribution pattern of temperature, quantile regression (Chamaille-Jammes et al., 2007) of monthly temperature data of a few stations for the period 1950-2007 have been done. It can be seen from the figure that increase in minimum temperatures has been steeper than the maximum temperatures, and the median temperatures have the steepest gradient. For Jessore in the southwest region, the maximum temperatures have been static, the minimum temperatures show a slight rising trend but the steepest gradient is with the median temperatures somewhat similar to Dhaka. For Bogra in northwest region, the maximum temperature has remained steady over the period, but for shorter periods a decline can be observed during 1950-80 and increase during 1980-2007. There is a rising trend in the minimum temperatures but the steepest gradient is in the median temperatures similar to Dhaka. For the southeast region temperature data of Rangamati has been analysed. It has been chosen because the station is different from others in that it is a hill station and in a rainforest. The maximum temperature in Rangamati actually shows a decline. The minimum and median temperatures follow the same trend as in Dhaka. From quantile regression of temperatures of different hydrological regions it appears in general that the maximum temperatures have not changed much, the minimum temperatures show a slight rising trend, but the number of warmer days in a year have increased significantly.

Source of Information: 2nd International Conference on Water & Flood Management (ICWFM-2009), BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The rising temperature in Bangladesh appears to be the direct consequence of climate change. Climate change may also affect rainfall though it has not been found to be statistically significant yet. Perhaps the most important impacts of climate change in the context of Bangladesh is sea-level rise and reduced availability of freshwater. Sea level will continue to rise in this century and beyond even with emission control and mitigation measures. Bangladesh being a deltaic region is very vulnerable to sea-level rise. Combating sea-level rise will perhaps be the greatest challenge that Bangladesh would face in not so distant future. Unfortunately, the options are limited due to high population density, thick alluvial deposits, gentle terrain and lack of resources. If population migration is an unavoidable alternative, it is perhaps high time that the planning process is started in right earnest.

There are reasons to believe from evidences elsewhere in the world that global warming is contributing to more frequent occurrences of extreme climatic events. Figure 3 shows the number of disaster scale floods and the number of destructive tropical storms that occurred in Bangladesh over the years. Data for these two figures are obtained from EM-DAT (The OFCA/CRED International Disaster Database, Brussels, Belgium). Both figures show a rising trend.

Knowledge Management: Report/Proceedings